The present invention relates generally to machining tools and more particularly to a machining tool which performs two or more machining functions, such as drilling and countersinking or to machining tools with removable pilots.
Drilling tools are commonly used to drill a hole in an object for receiving a fastening element, such as a bolt, to secure another part to the object in which the hole was drilled. It is oftentimes desirable to countersink the top of the hole or to spot face the flat surface area around the top of the hole to effect a close mating relation between the object in which the hole is drilled and the mating part bolted to said object. It is also desirable to combine the drilling function in one continuous operation with the countersinking function or spot facing function or both. To accomplish this combined operation, a combined drilling and cutting tool is used. This tool comprises a drill bit mounted on a rotatable holder on which a cutting element of some type is mounted or permanently attached in predetermined relation to the drill bit. The cutting element may perform the countersinking or spot facing functions or both.
There are some applications in which the cutting edge of the cutting element must be maintained a fixed, predetermined distance from the tip of the drill bit. This is to assure that the function performed by the cutting edge of the insert occurs on a surface spaced the correct distance from the bottom of the hole drilled by the drill bit. If the cutting edge were not maintained a fixed, predetermined distance from the tip of the drill bit, the object undergoing machining by the combined tool would be incorrectly machined. If the distance were too short, the hole would not be drilled to the proper depth when the countersinking or spot facing operations were completed. On the other hand, if the distance were too long, then, when the hole was drilled to the proper depth, the countersinking or spot facing operations would not be completed, and, in order to do so, the hole would have to be drilled to a greater depth than desired.
There are other applications in which the cutting edge need not be maintained a fixed, predetermined distance from the tip of a drill bit (e.g., when the hole is drilled all the way through the object being machined), but even in these applications, the cutting edge must be maintained in a fixed, predetermined axial position in relation to other parts of the machining tool or to some surface on the object being machined, or both.
In conventional machining tools in which both drilling and cutting operations are combined, the cutting element is usually of a relatively permanent nature, and, when the cutting edge thereon becomes dull, the element is removed to sharpen the cutting edge, when the cutting element is a removable insert. When the cutting element is permanently attached to a larger assembly, the entire assembly must be removed from the rest of the machining tool to sharpen the cutting element. After the cutting edge has been resharpened, the insert is replaced on the tool or the assembly to which the cutting element is permanently attached is replaced, and the cutting edge must then be correctly repositioned in relation to the drill tip or other portion of the holder or the workpiece. Because the dimensions of the cutting element are different than they were before the cutting edge was resharpened, due to the removal of material at the cutting edge in order to resharpen it, the job of correctly repositioning the cutting edge in relation to the drilling tip or the like is a difficult, time-consuming and tedious operation. In addition, time and effort are spent in the resharpening operation for the cutting edge.